1. Field of the Invention
This invention relates broadly to a safety system for protection of persons or objects from injury by being struck by power operated sliding doors. More specifically, it is particularly suitable for use with elevator doors and is presented accordingly.
2. The Prior Art
Protective devices have been proposed from time to time to minimize the danger inherent in automatically operated power sliding doors, where no attendant is present to act as a guard against persons being struck by the doors. The simplest and least effective of these is found on subways and city buses, and consists only of a collapsible rubber bumper along the door edge to cushion the impact when a person is struck or caught. Beyond this non-preventive approach are devices which attempt to prevent injuries by minimizing or eliminating contact between the doors and persons using them.
One such device has commonly been used on elevators in many forms, the so called retractable safety edge. It consists of a strip of rigid material, usually metal, covered at times with rubber or plastic, mounted adjacent to the elevator car door on pivot arms which allow its movement relative to the door. Through various arrangements of mechanical coupling, the safety edge is caused to precede the door edge by a small distance while the door is closing. Subsequent pressure against the device opposite to the direction of closing causes one to two inches of movement relative to the car door, and actuates a switch to effect stoppage and reversal of the door. Variations of the device have sought to refine it (see U.S. Pat. No. 2,687,455) but in substantially all cases the retractable safety edge requires contact with an object in its path in order to work, is easily damaged because it precedes the car door, and is generally poor because the combined inertia of the car door and the hoistway, or building, door coupled to it is often sufficient to carry both doors forward many inches after first contact with the safety edge. Further, the hoistway door is not normally supplied with a safety device, is located five to six inches apart from the car door, and consequently can strike a person in its own path before that person can engage the safety edge on the car door.
In order to improve the efficacy of the retractable safety edge, various forms of photoelectric light beam controls have been employed along with it, patterned after the methods of U.S. Pat. No. 1,947,079. Persons or objects using the doorway must interrupt a beam of light aimed horizontally across the doorway at some specific height, thus producing an additional control signal to that of the retractable safety edge. It has been the usual practice to position the one or two narrow light beams of this method to operate just outside the car door or, in certain cases, just inside. In either situation only moderate improvements in safety have been evident. It has still remained possible for persons or objects to miss the light beams completely, whereupon arms, legs or briefcases are then caught by the door at some height other than that of the light beams. As before, the hoistway door in this situation has remained unprotected.
In recent years several versions of an "electronic" device have been proposed to replace both the retractable safety edge and photoelectric controls. U.S. Pat. No. 2,601,250 and later patents trace the evolution of this device, which employs an antenna-to-ground circuit. The capacitance of the circuit is altered by the influence of some significantly large electrically conductive object brought into close proximity thereto. In theory these devices can be adjusted to respond to a variety of sizes and characteristics of the objects they are to detect, or can be adjusted in sensitivity to control their detection range, or can be adjusted and compensated to nullify effects from variations in hoistway doors, spacing, humidity and similar detrimental factors.
A study of related art covering these "electronic" devices exposes the difficulty of developing a single configuration capable of handling effectively all of the environmental factors necessary for proper operation. The predictable result has been complex and costly mechanisms which require undue care during and after installation and which usually demand extensive changes in existing elevator installations before they can be used to replace older existing safety devices. Further, extending the application of these "electronic" devices to provide protection for the hoistway doors requires fitting out each hoistway door at every building landing with its own additional apparatus. Clearly such systems are not well suited to the majority of situations where protection is needed.
A recent invention covered by U.S. Pat. No. 3,367,450 addresses the problem obliquely by using the Doppler shift in frequency principle to detect whether persons might be moving toward or away from the doorway opening, then using that information to hasten or delay door closing. Unfortunately, the requirement for fairly rapid motion of the person being protected does not cover stationary or slow moving feeble persons, or objects directly within the door opening, and that invention accordingly specifies additional use of some other standard protective device such as the retractable safety edge or one of the "electronic" variety.
In order to improve the general safety of persons using doorways served by powered sliding doors, and specifically to improve both the safety of elevator passengers and other load without undue complexity of equipment or delay in elevator service speed, information must be generated concerning the position of persons or objects in or near the doorway path including the path of the associated hoistway door, without regard to whether those persons be moving or still, leaving or entering, electrically conductive or not, but with due regard to whether or not at any point in the door travel they are endangered. Such information is enhanced if the actual distance from the advancing door or doors to the person or object is known, for a person directly in line with the door may not actually be considered as endangered until it moves sufficiently close to him. In commercial office buildings, where speed of service is important and where passengers are predominantly able-bodied adults, this is particularly true and it is important to put the door into motion to herald imminent departure of the car. However, in nursing homes and hospitals the definition of total safety may well require the doors to remain open and unmoving if a person is anywhere within the general doorway, for example, a situation where a feeble person using a walker or crutches timidly approaches the elevator car, or where a stretcher is being moved.